An aeolian sediment pulse at c. 28 kyr BP in southern Tasmania

Abstract

Thick aeolian deposits are uncommon in Tasmania but a 7‐m‐thick aeolian deposit containing two stratigraphic breaks, including one palaeosol, occurs as a gully infill at Cradoc Hill, 5 km east of the lower Huon River floodplain in southern Tasmania. The deposit was sampled at six depths for dating by thermoluminescence (TL) techniques. The entire deposit gave TL ages in the range 25–32 kyr BP (mean 28 kyr BP). One date of 41.4 kyr BP was discounted as being probably erroneous. In contrast to loess deposits of similar thickness in New Zealand, which have been dated and correlated with entire glacial periods, the Cradoc Hill aeolian sediments are interpreted to have been deposited in two stages over a relatively short time. As the prevailing winds in the region are westerly, the aeolian material is presumed to be derived from the Huon River floodplain in the vicinity of Egg Island, when the floodplain was occupied by a braided river; some of the sand component may also have been derived from locally outcropping sandstone rocks. Aeolian sediments of this age have not previously been recognised in Tasmania. A significant climate event that might explain a short and intense period of river aggradation and aeolian sediment supply has not been noted in either the pollen or δ18O record. An alternative explanation for the erosion and subsequent aeolian deposition is that it resulted from natural or human‐lit fires. Aboriginal settlement of Tasmania began around 35 kyr BP and the earliest recorded human settlement in the Huon catchment occurred at 28–29 kyr BP. A major erosion event in the mid‐Huon Valley also occurred at about this time (27–29 kyr BP). Thus, Aboriginal settlement in the Huon catchment, erosion in the mid‐Huon Valley, and deposition at Cradoc Hill are approximately contemporaneous. As older aeolian deposits are not present at Cradoc Hill, it is suggested that Aboriginal burning of vegetation rather than climatic influences may have caused both the middle Huon erosion event and aggradation downstream at about 28 kyr BP, providing a source of silt and fine sand which accumulated downwind, together with sand from local sources, as gully‐infill sediments. We therefore suggest that as Aboriginal people reached southern inland Tasmania they may have had an influence on landscape stability, river morphology, and aeolian dust supply. This suggestion requires corroboration from other sites.